In an attempt to understand the principles which underly protein to nucleic acid binding, to help elucidate the bases for specificity in such interactions, and to compare protein to RNA with protein to DNA binding, I plan to study the structures of various proteins and their complexes. X-ray diffraction methods will be employed on single crystals if possible, and on paracrystalline fibres where necessary. Present knowledge of nucleic acid sequences is rapidly expanding. However, sequences alone are largely uninterpretable. They can presumably by interpreted correctly, and the principles of protein- nucleic acid binding can be deduced, once crystal structures become available for appropriate proteins. X-ray crystallographic methods are now at an advanced level of development, where they should no longer be held in awe. Rather, it should clearly be recognized that a wealth of information lies dormant in unsolved protein structures, and that many interesting proteins can be crystallized and solved with reasonable effort. Thus, a dedicated program for gene-rating crystallographically suitable specimens is logically sound, technically feasible, and is necessary to achieve the goals outlined above. Specific projects proposed herein are aimed at producing suitable crystals of methionyl tRNA formyltransferase and/or its complex with met-tRNAF, and any or all of the histones F2b(II), F2al(IV), F2a2(IIbl), and F3(III) either individually or as aggregates. A concurrent fibre diffraction study of chromatin (nucleohistone) and various partially depleted or reconstituted nucleohistones will proceed to provide some basis for understanding how histone proteins bind to DNA to form chromatin.